One's a former Vice-President turned environmental activist, the other's a fast-growing media brand owned by one of the world's biggest oil exporters. So why has Al Gore sold his TV channel to Al Jazeera?

In 2008, Al Gore, US Vice-President under Bill Clinton and climate change crusader, posed a question during a speech at an energy conference in Washington. Referring to renewable energy sources such as solar power, he asked: "What if we could use fuels that are not expensive, don't cause pollution and are abundantly available right here at home?"

One answer, in light of Mr Gore's decision to sell his Current TV channel to Qatar-financed Al Jazeera, is that it would cause sleepless nights for his new friends in Doha, who make their money by selling fossil fuels to the world. Their success had made them very, very rich – and also given Qatar the largest per capita carbon footprint in the world.

This inconvenient truth was omitted from the email announcing the deal, sent to Current TV staff on Wednesday by Mr Gore's partner in the broadcasting project, Joel Hyatt.

"As you may know, Al Jazeera is funded by the government of Qatar, which is the United States' closest ally in the Gulf Region, and is where the United States bases its Middle East Air Force operations," he explained, according to a copy of the email obtained by The Wall Street Journal; what he forgot to mention was the oil and gas business, which accounted for more than half of Qatar's 2010 GDP, according to estimates by Qatar National Bank.Mr Gore has long campaigned about the environmental damage done by fossil fuels (in the process earning a Nobel prize). Now he has first-hand experience of its economic benefits, after the Qataris reportedly paid around half a billion dollars for Current TV. Based on his reported stake of around 20 per cent, the former VP is expected to net around $100m (£60m) from the sale, a healthy gain on the $60m that Mr Gore and his partners are reported to have paid for the channel in 2004.